Геномын судалгаагаар 1871 онд Амстердам аралд үлдээсэн үхэр нь хувьслын явцад биеийн хэмжээ нь багасаагүй, харин үүсгэн байгуулагч үүлдрүүд нь анхнаасаа жижиг биетэй байсныг тогтоов.
Францын фермер 1871 онд Реюньон арлаас таван толгой үхрийг Энэтхэгийн далайд орших Амстердам аралд авчирч орхисон нь тус бүс нутагт том биетэй мал амьтны өрсөлдөгчгүй орчныг бүрдүүлжээ. Тус сүрэг 1952 он гэхэд 2000 орчим болж өссөн боловч өвчний улмаас тоо толгой нь буурч, 1988 онд дахин 2000-д хүрсэн түүхтэй. Уугуул зүйлүүдийг хамгаалах зорилгоор 2010 онд сүргийг бүрмөсөн устгасан бөгөөд өдгөө тэдгээрээс 1992 болон 2006 онд цуглуулсан 18 амьтны ДНХ-ийн дээж л үлджээ.
Матьё Готье болон түүний баг Molecular Biology and Evolution сэтгүүлд нийтлүүлсэн судалгаагаараа эдгээр үхрийн геномыг 31 өөр үүлдрийн үхэртэй харьцуулан шинжилжээ. Судалгаагаар сүргийн 73 хувь нь Европын Жерси үүлдрийн, 27 хувь нь Мадагаскарын зебу үүлдрийн удмынх болохыг тогтоосон байна. Эдгээр үүлдэр нь биеэр жижиг тул 1871 онд аралд ирсэн таван үхэр анхнаасаа жижиг биетэй байсан гэсэн дүгнэлтэд судлаачид хүрчээ.
Өмнөх судалгаануудад тус сүргийг нэг зуу гаруй жилийн дотор хурдацтайгаар жижгэрсэн гэж үзэж байсан бол генетикийн шинэ шинжилгээгээр байгалийн шалгарлаар биеийн хэмжээ өөрчлөгдсөн гэх нотолгоо олдсонгүй. Геномын мэдээлэл нь үхэр бүр богино биетэй байхтай холбоотой генийн хувилбарыг агуулж байсныг харуулсан байна.
Сүргийн геномд 33 хувийн цус ойртолт илэрсэн хэдий ч энэ нь сүргийн өсөлтөд сөргөөр нөлөөлөөгүй болохыг тогтоожээ. Судлаачдын үзэж буйгаар, сүрэг хурдацтай өссөн нь цус ойртолтын сөрөг үр дагаврыг даван туулахад тусалсан байна. Сүргийн зан төлөвийн өөрчлөлт нь зэрлэгшсэн амьтдын мэдрэлийн системтэй холбоотой генүүдэд илэрсэн байж болзошгүй гэж үзэж байна.
Дэлгэрэнгүйг эх сурвалжаас харах
↓Эх сурвалжийг нээх ↓
In 1871, a French farmer brought five cattle from Réunion to Amsterdam Island and abandoned them there. The island is a 55-square-kilometer volcanic dome in the southern Indian Ocean, with no predators and no competitors for a large grazing animal.
The cattle did well. By 1952, their descendants numbered about 2,000. A disease outbreak in the 1950s crashed the population, but by 1988 it had climbed back to about 2,000.
In 2010, authorities eradicated the herd to protect the island’s native species, and nobody collected biological samples. What survived were DNA samples taken from 18 animals during field campaigns in 1992 and 2006.
Those samples now challenge one of the herd’s best-known claims. In a Scientific Reports paper, Roberto Rozzi of the Museum für Naturkunde in Berlin and Mark V. Lomolino of the State University of New York argued that the cattle had shrunk to about three-quarters of their ancestral body size in slightly more than a century. By their calculation, that was more than an order of magnitude faster than any other reported case of island dwarfing in large mammals.
A genomic study in Molecular Biology and Evolution found no evidence that the cattle evolved to be small. Mathieu Gautier of INRAE in Montpellier led the work, and Laurence Flori of INRAE and Tom Druet of the University of Liège were joint senior authors. Their conclusion: the founders were most likely small from the start.
Amsterdam Island Cattle DNA Reveals Jersey and Zebu Ancestry
The 2017 estimate depended on what the founders looked like. Rozzi and Lomolino assumed the five animals descended from four French breeds kept on Réunion at the time, which together averaged 553 kilograms. They estimated the island cattle at about 410 kilograms, working from limb bones of 90 adults culled in 1988 and 1989. They also ruled out any zebu ancestry. The authors did acknowledge that without genetic data, they could not say how much of the size difference was inherited.
The newer study read that genetic record directly. The team genotyped all 18 sampled animals and compared them with 31 other cattle populations. They also sequenced the whole genomes of eight females sampled in 1992.
About 73% of the herd’s ancestry was European, with the closest match on the island of Jersey. The other 27% came from Indian Ocean zebu related to Madagascar cattle. That mixing dates to around the founding itself, which suggests the five animals already had mixed ancestry when they left Réunion.
Both of those source populations are short. Using 105 known height-related genetic variants, the team predicted each animal’s genetic potential for stature. The island cattle came out between Madagascar zebu and Jersey cattle, and well below Holstein. Every island animal sampled carried two copies of a gene variant linked to short stature, as did every Jersey animal in the comparison.
The researchers found no sign that selection had pushed the herd toward smaller bodies.
Genomes Confirm Five Founders and Rapid Herd Growth Despite 33% Inbreeding
The genomes support the historical record of the founding. Estimates of effective population size, meaning the number of animals actually passing on their genes, fall to about 4.5 individuals roughly 22 generations before sampling.
Inbreeding was high. On average, a third of each sequenced genome was inherited identically from both parents through a shared ancestor. Most of that inbreeding traced back to around the founding, not to recent generations, a pattern the researchers attribute to the herd growing quickly after the bottleneck. The modern Holstein and Jersey dairy cattle in the comparison showed more recent inbreeding than the feral herd.
The founders’ European ancestry also appears to have suited them to the island. When the team compared Amsterdam Island’s climate with the home regions of 31 cattle populations, the closest genetic fit was Jersey. The authors conclude the herd faced no strong climatic challenge. Most of the genes that did show signs of selection relate to the nervous system, which the researchers link to rapid feralization, as domestic animals changed their behavior and formed new social groups in the wild.
The paper describes a population that “thrived within a few generations in a seemingly inhospitable environment.”
Cattle Were Eradicated in 2010 to Protect the Amsterdam Albatross and Native Plants
The herd’s success had a cost for the island. By around 1950, according to the 2017 paper, grazing and trampling had heavily damaged the native vegetation, and much of it had been replaced by introduced plants, particularly forage grasses. The cattle threatened an endemic tree and the Amsterdam albatross, a seabird found nowhere else.
Managers acted in stages. Fences went up in 1987 and 1992 to restrict where the cattle could roam, and culling began in the late 1980s. The herd was eliminated entirely in 2010.
The genetics team does not argue the decision was wrong. The authors do write that feral populations carry unique genetic legacies, and that this raises ethical questions for conservation. They also note that the eradication happened without any effort to collect samples, so everything now known about the herd’s genes comes from the 18 animals sampled before it.
The island has since moved on without its cattle. In a January 2012 update, the Agreement on the Conservation of Albatrosses and Petrels reported that planting of the native island tree was continuing. The fencing that once held the cattle back had been removed the previous December, because it was no longer needed.
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